Physiological adaptation and metabolic property of earthworms in vermifiltration for liquid-state sludge stabilization using bulk stable isotope and specific fatty acid compound stable isotope values

The presence of earthworms in vermifilter (VF) led to the significant stabilization of sludge by enhancing the reduction in volatile suspended solids by 20.9%. The proliferation of earthworms feeding on the sludge was reflected by the observed increase of earthworm biomass, which indicated that earthworms adapt to VF environment well. Further investigation conducted using bulk stable isotope combined with specific fatty acid compound stable isotope technologies to determine physiological adaptation and metabolic property of VF earthworms. The observed injury of cuticle and the dense of goblet cells demonstrated that the earthworm was suffering from environment stress. However, earthworms could adjust their antioxidant enzyme systems to maintain their normal physiological function. Analyses of the bulk stable isotope and specific fatty acid compound stable isotope showed that the physical metabolism of earthworm hatchlings was more active than that of earthworm adults, which suggested that the increasing proportion of earthworm hatchings might be an effective way to optimize earthworm population structure in the VF system. Consequently, the improved treatment performance of sludge stabilization by vermifiltration was realized.